Wolfeman: got a tip for me? (Amp Tech)

[Lasse Lammert]

HEy, I've got this one amp which sounds extremely awesome, but the EQ is just a bit fucked up...
especially the mids, the lowest position of the pot is "1", that give a rather scooped sound (not too scooped), the problem is that everything above 2 is getting VERY honky and middy, around 3-4 it'll be telephone-like.

I'd like to change the range of the pot so that the lowest position sounds like the lowest position now (or even a bit more scooped would be nice), but the maximum setting should not be more middy then it is now when the dial is around 3-4 now....
will a change of the pot be enough or will I have to do something else?

thx

LL

 

[PaoloJM]

HEy, I've got this one amp which sounds extremely awesome, but the EQ is just a bit fucked up...
especially the mids, the lowest position of the pot is "1", that give a rather scooped sound (not too scooped), the problem is that everything above 2 is getting VERY honky and middy, around 3-4 it'll be telephone-like.

I'd like to change the range of the pot so that the lowest position sounds like the lowest position now (or even a bit more scooped would be nice), but the maximum setting should not be more middy then it is now when the dial is around 3-4 now....
will a change of the pot be enough or will I have to do something else?

thx

LL

What amp?
It'll depend on the tone stack style.
Sometimes a pot change will be enough, but you may want to change a cap too.
Remember that with a passive stack the mid frequency will probably shift slightly, you'll need to experiment to find a good compromise.
In the meanwhile download this http://www.duncanamps.com/tsc/, it'll give you a visual indication of each change and what different values will do.

 

[sprack]

If there's that little variation by 2-3 it almost sounds like its linear taper.

 

[PaoloJM]

If there's that little variation by 2-3 it almost sounds like its linear taper.

other way around, and it might well be the issue.

 

[Lasse Lammert]

it's a (heavily) modded Marshall (mod by Bogner).
it's nt the original Marshall tonestack anymore....so if I replace the mid pot with a log one it'll be more controlable already?
shall I try bigger or smaller pot values?

This amp really sounds fantasitc, it's just very difficult to control atm, all the good tones are with the mid pot between 1 (lowest position) and 2...everything above gets extremely honky, I'd really like to stretch that range much more to make it more controlable

 

[::XeS::]

Maybe you should add some other components to change the "filter"...like the condensers used with the guitar tone pots. But it's only the first idea that came in my mind

 

[SoundSpiral]

Have you thought of using an external eq on the FX loop?

 

[Lasse Lammert]

nah, don't wana cut honky mids just because the tone stack isn't designed properly...I'd rather fix the problem where it occurs tbh

 

[PaoloJM]

nah, don't wana cut honky mids just because the tone stack isn't designed properly...I'd rather fix the problem where it occurs tbh

I can help, and am happy to, but I'd need to know the tone stack schematic first, otherwise it's pure guess work.

A Log pot will make the problem far worse. Both Fender and Marshall style stacks use Linear pots for the mid pot. This would be what you're used to.
As I mentioned; if there a mistake made during the mod then there might be a log pot in there, in which case you want to swap it for linear.

Do you have a multi-meter? If so measure the resistance between the two outer lugs. Then wind the pot half way and measure from one of the outer lugs to the centre. If the value from outer to centre is either 90% or 10% (depending on the outer lug you picked) of the full value between the outer lugs then you've got a log pot and replacing it with a linear of the same value will help.

Even a close up picture of of the tone stack part of the board would tell a lot of what's in there and what needs changing.

 

[Lasse Lammert]

thanks, here are the pics:

I know, looks a bit chaotic, doesn't it

 

[Lasse Lammert]

The pot is a LINEAR 100k

 

[PaoloJM]

Ok. Check out that TSC program I sent you a link for.
Mid pots are generally between 10k and 25k linear.
If you change the value of either the Marshall or Fender style you see replacing a 100k brings you from mild scoop to honk central pretty quickly.
Go back to 10k or 25k and you're back to what I would call "normal".
To test try soldering a resistor across the outer lugs, say around 33k or 47k. That'll give an indication if that's the problem, and it's easy to undo if it's not.

 

[Lasse Lammert]

thanks heaps! gonna try that now

 

[Lasse Lammert]

k, that definitely helped (resulting in about max 25k now (33k parallel to the pot) it's much better but still not perfect, I think I'm gonna try a 10k).

while we're at it...
the other pots have got a similar but lesser problem (and the other way round), the treble pot is hardly doing anything until around 6-7, then it's jumping up...that's easier to deal with than what I had with the mid pot, but if it could be fixed equally easily....

the bass and presence pot have to be max'd to get enough bass and presence....my noob though coming from what the mid pot did would be: if I now raise the value of the bass pot it should give me more bass earlier..? I guess that's not how it works, is it ?

my settings now are:
pres: max
Bass: max
mid:2
treb: 7-8

I know, that looks like some black metal kid's settings, lol..but the resulting sound is "normal", so not like one would expect from just looking at the dials.
I'd like to get a sound like that from setting the pots "less extreme" if possible.

The Amp sounds great, but it's a bitch to dial in, What Bogner did sounds definitely good, but the way he designed the tone stack seems to be a bit fucked up tbh


There's no depth pot, so I'm thinking about tweaking the neg feedback a bit to get more "depth/oomph"

Unfortunately I can't use TSC as it's windows only

 

[Lasse Lammert]

Haha, got my old PC lappy to work again

damn, TSC is a great tool!

 

[Lasse Lammert]

I think I'm gonna try getting closer to the rectifier's tone stack with BMT:1M, 25k, 250k.

Also I'm thinking about increasing the load resistor from 500k (now) to 1M for increased bass response

gonna check the caps in the Bogner MArshall now

 

[psycle_1]

If you want more oomph, remove the negative feedback lead completely. If that is too much oomph, you could always add a pot or fixed resistor in after the fact. But removing it would be the easiest way to try it first. This in essence is how the Rectifier's Modern mode works, removal of the negative feedback loop.

 

[Lasse Lammert]

fuck, just tried to re-draw the tone stack of the Bogner Marshall...just to understand what's in there...it's a bit more complicated involvin a double pot (2x1M) for the bass)...
BAAAAAALLS

If you want more oomph, remove the negative feedback lead completely. If that is too much oomph, you could always add a pot or fixed resistor in after the fact. But removing it would be the easiest way to try it first. This in essence is how the Rectifier's Modern mode works, removal of the negative feedback loop.

yeah, thought about trying that.
....
atm I'm just trying to understand this amp's tone stack....seems to be a bit more complicated than the Marshall standard (although it seems to based on the Marshall tone stack, but it involves 6 resistors, 7 caps, and all with rather odd values )..the double bass pot is also confucing, lol

 

[Lasse Lammert]

The big advantage: the tonestack is neatly placed on a little PCB, so in theory I could send it to someone with a clue to turn it into something more usable ......anyone up for it?

 

[PaoloJM]

glad you seem to be getting somewhere. why not try another 33k over the existing one?

before you go to far with modding the stack; there seems to be a lot of components in there.
you sure there is not some kind of "voicing" switch on that amp?
can you find out more about the mod first?

what about posting some clips with the stack set to midnight and then various other setting so we can hear what it's doing?

what resistor is the "load resistor"?